If you Google for "Corny Keg" or "Cornelius Keg", you'll find plenty of vendors for used soda kegs and parts. I got mine from Beverage Elements.

Most vendors will do a pressure test prior to shipping and guarantee it will hold pressure. Mine unfortunately has a very slow leak around the pressure relief valve on the lid, working to get that fixed. Doesn't look like I can get at the rubber seal inside, maybe adding some o-ring lube through a port will help.

In leroy_sunset's post #87, that white plastic thing at the end of the hose is called a disconnect. They come in ball lock and pin lock versions depending on what type of posts are on the keg. When you put the disconnect on the input (gas) post, it opens the poppet valve in the post so you can fill it with air.

Technically, it doesn't matter which type you get so long as the disconnect and posts match. Coke kegs are pin lock, Pepsi and everyone else used kegs with ball lock posts.

Practically, it seems like used ball lock kegs are more common in the marketplace. I've also seen used pin lock kegs retrofitted to be ball lock. The little ball bearings in my ball lock disconnect work smoothly with my keg.

Ball Lock vs. Pin Lock —
Couple of things: The Quick Disconnects are different — Ball Lock disconnects use a steel ball that tightly secures it to the post. Pin Lock disconnects use a pin locking system to secure to the posts. Height — Ball Lock kegs are 25" tall and Pin Locks kegs are 22"… a little shorter and fatter version of the keg. And NO that's not why more people like Ball Lock kegs…it's because they have a 'pressure relief valve' built in — now don't you wish you could install those into you—know who? Both types hold 5 gallons. Pressure Relief Valve — True Ball Lock kegs have pressure relief valves built into the lid, and Pin Lock kegs rarely do (maybe 1 out of 20). With Pin Lock kegs there are a few ways you can release the pressure including using a spare gas disconnect put onto the post and it's the same thing. Both great kegs!

Check out the photos in post #87. That hose with the white-colored nylon disconnect on one end has the brass tire valve on the other end (even though that isn't shown in the last two photos).

To add pressure, first close the lid. Then push the disconnect onto the post labelled "IN". The valve in the post will now open. Now you have a path to get air into the keg. Attach an air pump to the brass end and start pumping in air. You can remove your pump and attach a tire gauge to see if the pressure's at the level you want. When the pressure level is where you want it, just pull the disconnect off the post and the valve in the post will close. That's all there is to it.

The post labelled "OUT" doesn't need to be used or connected to anything.

Places that sell used kegs will also sell parts like the white disconnect you need. You can buy the hose from a hardware store and the brass tire valve from an auto parts store. Most 1/4" vinyl hoses will handle up to 50psi so you don't need to get the heavy duty hose show in post #87. The standard hose will be easier to use.

To remove pressure ... the previous post was correct. Most ball lock kegs come with a pressure relief valve on top of the lid. So just flip a lever or pull a ring and pressure will be released. For pin lock kegs without a pressure relief lid, you can either use a screwdriver blade to press down on the "IN" post to open the valve, or you can use a spare disconnect and put it on the post.

So you have a tradeoff ... the ball lock keg with pressure relief valve lid is more convenient to use when releasing pressure, but it's one more valve to worry about going bad. Your choice.

There are tons of people selling used kegs on the internet (just google "corny keg"). I suggest finding one near you because the shipping costs can sometimes be high.

I also had to replace the dip tube o-rings under the gas and liquid posts. A soap-bubble test revealed leakage. To get the ball lock posts off, you typically need a large 7/8" or 11/16" wrench or deep socket (for pin-lock, you need a special tool sold by microbrewing sites). Sometimes, you need the wrench/socket to have 12-points instead of 6-points. My gas post was 7/8" with a 12-point star pattern (unusual for a Cornelius ball lock keg like mine, the star pattern is usually found on Firestone ball lock kegs).

I found this handy ratcheting box-end wrench at Sears with 7/8" and 11/16" ends. Perfect for this job and cheap (on sale now for 8.92)!

If you get more than one keg, try to get the same brand so you can share parts (Cornelius, Firestone, etc.). The threading on the posts and the height of the poppet valves are different depending on the brand.

Here is a great link that lists the different thread types and shows pictures of the different poppet valves:

Have any of you Cornelius (corny) keg users found a more efficient way to get balls into and out of the kegs? I have been picking up three per hand to put them in which goes relatively quickly but getting them out and into my pickup basket is a PITA. I hold each keg up at about a 45 degree angle with mouth opening pointing downward and reach in to the keg through the opening and pull out balls. Sometimes, but not often, a ball or two will drop out on its own but for the most part I am extracting each ball or couple of balls by hand.

Can you replace the liquid dip tube with a shorter gas tube? I think the liquid tube will take up space for balls.

Click to expand...

It does and you could but I haven't. You could just remove the liquid out tube and cut it all off if you weren't worried about ever using the kegs for soda (or beer in my case) again.

When I was using my kegs for storing homebrewed beer I actually pulled the liquid pickup tubes out of some of them and cut about an inch off the bottom so they would not pick up any yeast sediment which had collected on the bottom. If you are a patient homebrewer you don't have to do this as the yeast will eventually pack itself enough so that it won't get sucked up but I wasn't very patient. Me want beer now, dammit.

Have any of you Cornelius (corny) keg users found a more efficient way to get balls into and out of the kegs?

Click to expand...

I've only pulled balls out twice while resolving my pressure issues but had the same experience as you. I might try sticking in an extraction aid ... imagining something like a cabinet hinge that folds in one direction (so you can push into the balls) and locks in the other (so you can pull on the balls) ... mounted to a long handle?

I've only pulled balls out twice while resolving my pressure issues but had the same experience as you. I might try sticking in an extraction aid ... imagining something like a cabinet hinge that folds in one direction (so you can push into the balls) and locks in the other (so you can pull on the balls) ... mounted to a long handle?

Click to expand...

Thanks that is worth a try. Like I said right now I just hold the keg in one arm and use my other hand to pull out balls which works but I'd like to find a faster way if there is one.

FYI ... the Physics Department at the University of Illinois contacted Wilson Sporting goods and found out that the internal pressure of Wilson's tennis balls is 27 psi (which is almost twice atmospheric pressure):

The note at the bottom of the link says that 27 psi is absolute pressure, not the gauge pressure. I believe this means pressurizing your keg to anything over 14 psi as read on your gauge should begin to repressurize old balls.

Just wanted to give a shout out for the excellent photos and description. I followed your lead and am now fermenting my first batch of balls

I got a used 5-gal Cornelius keg from Beverage Elements with ball locks on the gas-input and liquid-output fittings (those shiny round "posts" on top of the keg). Also bought the necessary plastic quick-disconnect for the gas fitting.

The gas fitting internally has a spring-loaded pressure valve (a "poppet") that lets air into the keg from your air pump. Normally both the gas and liquid fittings are shut tight when there isn't a disconnect attached.

Most ball lock kegs have a manual pressure relief valve on top of the lid and this comes in handy when it's time to pull the balls out. Pin lock kegs usually don't come with that kind of lid, although they can be retrofitted easily and are sometimes sold that way.

I used the same air tank schrader valve shown in leroy_sunset's photo. Instead of using the high pressure hose (usually rated to 200+ psi) I used regular vinyl hose that's good up to 50 psi). The tip to heat the 1/4" ID hose before inserting the schrader valve is a good one since its a very tight fit. The hose clamps are stainless steel, 5/16" wide, 7/32" to 5/8" OD.

After pumping air into the keg, I attached a tire pressure gauge to the schrader valve to check the pressure, then removed the disconnect and its hose (the poppet seals the gas fitting).

I'm pressurizing at 28 psi right now (150 strokes with a bicycle floor pump). Like others, I also heard a few "popcorn popping" sounds from inside the keg when pressure went over about 25 psi.

Click to expand...

I'd like to build one up myself as well.

Can someone post an image of the final product? For some reason I only see parts.

Pardon my lack of knowledge of basic physics, if I understand correctly, since there are two inlet into the corny keg, one pumps air (with a air compressor) into the keg, and the other inlet let's the air out. Since there's a gauge on the pump, we can accurately read the pressure, right?

So there is no need for a venturi style pump then?

thanks for the help. Also, how long does the balls maintain a good bounce? I would figure the rubber inside the balls can not take long term stress of being pumped, deflated, and smacked by a racquet.

All you need is a bicycle or car tire style pump. I'll post a photo of the whole thing if nobody else does by the end of the day.

I only use one of the posts (the one marked "IN"). Grab your hose that has the slip-on post fitting on one end and the threaded brass schraeder tire valve on the other. Slip the post fitting over the IN post of your keg. Now attach an air pump to the tire valve and start pumping in air. When done, remove the post fitting - the "poppet valve" inside the post will close to keep the air in.

If you want to check air pressure later, slip the hose onto the post again. Then attach a pressure gauge to the tire valve - just like checking pressure on a bike or car tire.

having said that, why would you use old balls for serving practise? hitting with old balls can cause damage to your shoulder and elbow.
so why risk using said balls when you are hitting the ball as hard as you can during your serve?

Click to expand...

Leaving the question alone whether it is wise to hit a serve as hard as you can during practice what is the problem using old balls for serving practice?

This should be a great option for people with ball machines. I was hitting all out today with some Tretorn Micro-X balls, and even though they're not as hard as other brands, I would have preferred 150 pressurized balls. hmmm.... (he says as he rubs his sore shoulder)

For filling the keg with air and for measuring pressure with a tire gauge, the pigtail you want to make is shown below. I picked up the 1/4" ID PVC tubing and small stainless steel hose clamps from a hardware store. The schraeder tire valve was purchased from an auto parts store:

The next photo below shows the end of the pigtail that attaches to the keg using a gas post fitting (called a "disconnect"). I purchased the disconnect from an online home brewing supply shop. Note the gas post disconnect has little spring-loaded ball bearings which are used to secure the fitting onto a recessed groove machined into the gas post. Kegs with this type of post are called "ball lock kegs":

This shows the pigtail connected to the input gas post of the keg. The output liquid post (on left side of the keg) where pressurized soda/beer would come out is not used. It would be possible to permanantly attach another pigtail with a pressure gauge to the output post, but then you'd have yet another thing that could leak (a negligible amount of pressure is lost should you want to attach the pigtail to make a pressure measurement after filling the keg). So you really only need to purchase a disconnect for the input post. They are usually color-coded gray. Disconnects for the output liquid post are usually color-coded black:

Next to the keg is a small light-duty electric air pump I use to inflate car and bike tires. It works well with the keg. You can use a bicycle foot pump if you want to get a nice workout

It's really a pretty easy project to build. The thing that took me the longest was Googling for places to buy used soda kegs and parts, and understanding what all the parts are. Be sure to buy spare O-ring seals if new ones aren't included with your used keg. My tiny O-ring that sits inside the gas input post was responsible for a small leak - very easy to replace. You can buy a tube of food-grade lubricant to lube your seals, all the brewing outfits sell them.

Hope these photos help. Thanks to leroy_sunset for his informative post that got me started.

^^ Oh man I'm still using the same tennis balls from last year in my ball machine because of the kegs. The felt may be down a little, but the ball is hard and still use them for warming up. They last about a week outside of the keg before needing to be topped back off a little.

... if I understand correctly, since there are two inlet into the corny keg, one pumps air (with a air compressor) into the keg, and the other inlet let's the air out.

Click to expand...

In case you haven't already figured it out, the easiest way to release pressure when you want to use the balls is to pull up on the manual pressure relief valve ... that's the ring attached to the top of the lid shown in the last photo.

This is one of the best reasons for getting a "ball lock" keg (aka "Pepsi" keg) instead of a "pin lock" keg (aka "Coke" keg). Many of the pin lockers don't have that manual release valve. You do see a mix of kegs and lids in the used market however.

Also, how long does the balls maintain a good bounce? I would figure the rubber inside the balls can not take long term stress of being pumped, deflated, and smacked by a racquet.

Click to expand...

I agree with IDrinkYourMilkshake, balls hold pressure for about a week. I've only been doing this for 6-months but the balls keep on bouncing back ... pun intended

I've been using a mix of Costco Penn's, Penn ATP's, and Dunlop Grand Prix's. They all work for me. A small fraction of the balls won't re-pressurize, but I haven't noticed any trend as far as brands go. Pressurizing between 25-30 psi works for me. Right around 30 psi, you'll start hearing a muffled noise coming from the balls sorta like popcorn poping!

I do the Cornelius keg recharging thing too fwiw. I have three kegs full of balls right now. Watch craigslist for kegs and sometimes you can find deals on them but there are also plenty of places online that sell reconditioned ones for ~$50. Make yourself a hose connector and get an auto airpump and you are good to go. I own 6 kegs now--3 for tennis balls and 3 for homebrewing.

I noticed we both have the kind of relief valve that is replaceable. For those looking to get a keg, if you have a choice, try not to get the kind of lid that has a flip-lever instead of a pull-ring. AFAIK, the former isn't replaceable.

I don't recall where I found this, but here's a nice breakdown of all the parts of a ball-lock style keg. Useful in case you ever need to rebuild your keg or buy parts. I left the dip tubes in.

And to do a pressure test after getting a keg, first pressurize it. Then take a rag dipped in water + dishwashing soap and liberally swipe around the lid, gas & liquid posts, and relief valve. If you see tiny bubbles, you've got an air leak. Sometimes reseating the lid or lubricating the O-rings will fix the leak. Other times you'll need to replace an O-ring, relief valve, or poppit valve.

Using a corny keg as ball pressurizer is brilliant, cost effective solution guys! I'm an old homebrewer and have several laying around, so I'm totally psyched.

I just have one comment at this point concerning the keg type: Yes, the pressure relief valve is very nice on the ball lock keg style, but it is also VERY easy to release the pressure on a pinlock keg using a a small screwdriver. You can simply push down on either the air intake or outlet valves to release the air. If you can find pinlock kegs for significantly cheaper than balllock kegs, then I would go with the cheaper one--it's really easy and trivial to release the air in a pinlock keg and this really isn't a significant issue, imo.

Using a corny keg as ball pressurizer is brilliant, cost effective solution guys! I'm an old homebrewer and have several laying around, so I'm totally psyched.

I just have one comment at this point concerning the keg type: Yes, the pressure relief valve is very nice on the ball lock keg style, but it is also VERY easy to release the pressure on a pinlock keg using a a small screwdriver. You can simply push down on either the air intake or outlet valves to release the air. If you can find pinlock kegs for significantly cheaper than balllock kegs, then I would go with the cheaper one--it's really easy and trivial to release the air in a pinlock keg and this really isn't a significant issue, imo.

Click to expand...

I as well use a corny keg to extend the life of my balls. But I took a different approach, where I drilled out the emergency relief value and slipped a long stem tire valve through it, and it works like a charm with no air leaks. This way I can use my air compressor and pressure gauge without any hassle. It holds about 50 balls or so.